Radar level gauging (RLG) to measure the level of a filling material, such as a liquid or a solid like a granulate is an increasingly important method for level gauging in tanks, containers, etc. In RLG, continuously emitted radiation, and in particular FMCW, is used for most applications. However, pulsed RLG is becoming a more widely spread method for industrial level gauging, due to its simple and cost effective microwave components. The pulse in a pulsed RLG can be modulated by a carrier frequency, typically 6 or 24 GHz, or be an unmodulated DC pulse. In the latter case, it is common to use some kind of transmission line, such as a coaxial line, twin line, etc., sometimes referred to as a probe, in order to guide the electro-magnetic signal through the material in the tank where it is reflected by one or more interface surfaces (such as air/liquid) between different parts of the tank content. In the former case a transmission line or wave guide can also be used, but generally an antenna is used to freely emit radiation in the form of a vertical radar beam which is reflected at possible interface surfaces.
However, pulsed radars typically have lower sensitivity compared to frequency modulated continuous wave (FMCW) radar. The sensitivity, i.e. the ability to detect weak reflections, is an important virtue for any RLG as a high sensitivity may enable the use of a smaller antenna or a longer transmission line, all other parameters held constant. Accordingly, various attempts have been made to improve the sensitivity of pulsed RLG systems. For example, US 2006/0055591 by the same applicant discloses an improved type of directional coupler, providing increased sensitivity to the system.
However, there is still a need for alternative or additional means for improving the sensitivity of pulsed RLG systems.